Because price cutting is necessary, is why.
In the UK the train operators have competition among them. In Poland the government doesn't want to allow independent operators to the national tracks. The only exception is when local governments, sometimes being more sensible then the national one, choose a private operator in a tender to operate the local trains.
With the national train operators it is more or less like with the national mining companies - for sure you heard about the recent strike in one of them.
The government - as an owner of different companies, like railway operators, mines and so on, does little to make them competitive. In case of railway it's easy to block any competition on the tracks. Of course, it is quite short-sighted, because many people resign from trains at all and they use private cars (which results in increased air pollution and road traffic) or bus connections (especially since PolskiBus appeared). But it's enough for the period of office of the given government. They don't care of what will be later - it doesn't bother them. What is important is to find jobs for their family, relatives, acquaintances in form of well-paid managerial positions (even if they know nothing about management - and it's the next reason why it looks as it looks).
The next thing is to keep the existing employment in the national companies. Even if they give no profit and the government must even pump extra money into them (yes, from people's taxes). In national companies it's quite common - usually it's a reminder from the communist times, where the basic rule was that the country must give job to everyone. To make these companies bring profit, the only way are massive layoffs. But here, there are two problems. Firstly, it would set people against the government. Secondly, it would result in huge social problems. If somebody was educated as a miner from the very beginning, he won't find another job. After being made redundant, he will stay unemployed probably for the rest of his life. So the government is often saying about "restructurisation" of the national companies instead. Which in practice means that they fire a few people on managerial positions, employ new ones (this means, of course, fellow politicians or family members) and that's all.
This is the problem with all the national, and generally speaking, public companies (it includes also those owned by local governments, for example by a city). Instead of making the company competitive, the authorities don't allow any competition to appear. Or, at least, they think they don't allow, but it's not fully possible. Why? It's simplier. What is most important for them - they are saving the workplaces. Which are usually not needed, but it turns out that people can bear too high taxes, but at the same time they cannot bear massive layoffs in public companies.
Of course in case of the fields in which it's totally impossible to exclude competition, like in case of mining, the company finally goes bankrupt. Because it turns out that it's cheaper to import coal from Russia or Czech Republic than to use one produced in Poland. Although it was always said that the coal is the greatest wealth of our country.
Conclusion - I don't know how it looks like in the other countries, but the national or public ownership of companies belonging to any field of economy isn't a good idea in Poland. In theory it should be more profitable than when the company is private - there is no "capitalist" who takes some of the money for himself. But it doesn't work so in reality.
About the people that resigned from trains at all - it is depicted quite well by the recent TV commercial of PKP Intercity: "Kto z Państwa jechał ostatnio pociągiem PKP?" - "Who of you has recently ridden a PKP train?".
I will try to translate it.
There is a meeting of parents and the teacher (supervisor of a class) at school.
Teacher: At the end, the issue of the school trip.
Parent 1: I don't know if it's a good idea for our children to go by train. Have any of you recently ridden a train?
Parent 2: Excuse me, but have any of you recently ridden a PKP train?
Parent 3: But each train is PKP!
Parent 2: And each man with a pitchfork is Poseidon!
Parent 3: Who?
And then the lector: We are one of the biggest Polish transport operators, but not the only one. Therefore, not all the trains are PKP. See how we are changing and choose a journey with our trains!
Even producing such a commercial is a great progress in a company such as PKP Intercity. They are, at least, trying to recover the lost customers. It is improving - but very slowly, and maybe not in case of the PKP SKM company, which really has no competition (unlike the PKP Intercity, operating on long-distance routes, where there are also for example PolskiBus coaches).